1. Field of the Invention
This invention relates to a magnetic recording substance and more particularly, it is concerned with an improvement in the back layer of a magnetic recording medium such as broadcasting video tapes, helical video tapes and high density recording tapes similar thereto.
2. Description of the Prior Art
In order to improve the running property of a magnetic recording substance, it has hitherto been conducted to roughen the back layer of the magnetic recording substance, for example, by one of the following methods:
(1) SANDBLASTING THE BASE SURFACE REVERSE TO THE MAGNETIC LAYER,
(2) COATING THE REVERSE SIDE TO THE MAGNETIC LAYER WITH A POWDER OF CARBON BLACK, GRAPHITE, KAOLIN, BARIUM SULFATE, SILICON DIOXIDE, TITANIUM OXIDE, ETC. WITH A BINDER, AND
(3) CONTROLLING THE TRANSPARENCY OR LIGHTNESS OF THE COATING LAYER OF THE ABOVE DESCRIBED METHOD (2) TO DETECT COATING DEFECTS AND TO IMPROVE THE MARKING PROPERTY.
In these known techniques, the method (2) using a layer composed of a powder of carbon black, graphite, titanium oxide, etc. in a binder has the following problems:
(1) When the surface of a magnetic layer is smoothened mirror-like as in video tapes, the scattering of the edges of a tape wound takes place.
(2) When a tape is subjected to fast forward or sudden stopping, the tape loosening takes place.
(3) The surface unevenness of the back layer affects a magnetic layer to increase the modulation noise.
These phenomena become remarkable with the increase of a tape width or a tape speed and thus appear often in the case of using a long tape with 2 inch width .times. 2195 m or 2 inch width .times. 2880 m in a high tape speed recorder such as AVR-1 of Ampex type VTR.